Conventional optical devices, e.g., optical pickups in compact disc (CD) players or optical disk drives or magnetooptical disk drives, are complex in their overall arrangement, require complicated optical layout settings, and cannot easily be mass-produced because optical components including gratings, beam splitters, etc. are individually assembled.
For example, an optical pick for use with an optical recording medium such as an optical disk, for example, which is shown in FIG. 15 of the accompanying drawings, has a light source 51 such as a semiconductor laser diode or the like for emitting a light beam. The light beam emitted by the light source 51 is introduced through a grating 52 into a beam splitter 53 and passes therethrough. The light beam travels through a collimator lens 54 and is focused by an objective 55 onto a recorded area of an optical recording medium 56 such as an optical disk. In FIG. 15, the dot-and-dash line "c" represents an optical axis from the light source 51 to the optical recording medium 56.
The light beam reflected by the optical recording medium 56 passes through the objective 55 and the collimator lens 54, and is reflected by the beam splitter 53 off the optical axis "c" to travel through a concave lens 57 and a cylindrical lens 58, which focus the light beam onto a detector 59 such as a photodiode (PD) or the like.
Another optical device, which is shown as part of the optical pickup of a reflective optical scanning microscope in FIG. 16 of the accompanying drawings, has a light source 51 which emits a light beam that is reflected by a beam splitter 53. The reflected light beam is focused by an objective 55 onto the surface of a specimen 60 over a focal plane 61. The light beam reflected by the specimen 60 travels through the objective 55 and the beam splitter 53, and either is detected by a detector positioned in a confocal point or passes through a pinhole 62 and is then detected by a detector 59 disposed behind the pinhole 62. The condition of the surface of the specimen 60 can be detected when a stage that supports the specimen 60 or the irradiating light beam is relatively scanned as indicated by the arrow "s".
In the above conventional optical devices as optical pickups, in order to prevent the reflected light beam from returning to the position where it is emitted, i.e., the light source, the beam splitter is disposed between the light source and the irradiated medium or a hologram is disposed as disclosed in Japanese laid-open patent publication No. 1-303638 for separating the reflected light beam, i.e., the light beam returned to the light source, from the optical path toward the irradiated medium. With this arrangement, however, the intensity of light that is detected by the light-detecting device is reduced.
If any of the above optical devices is assembled as a hybrid structure on a semiconductor substrate such as of Si or the like as shown in Japanese laid-open patent publication No. 2-278779, then a strict level of accuracy for alignment will be required.
The present invention has been made to simplify the structure and reduce the overall size of an optical device such as an optical pickup, for example, to simplify the process of manufacturing the optical device, to increase the reliability of the optical device, and to increase the intensity of returning light toward a light-detecting device, i.e., the intensity of detected light, so that the optical device will produce an increased output, have a light source of low power requirement, and consume a reduced amount of electric energy.